RFR: 8365571: GenShen: PLAB promotions may remain disabled for evacuation threads

[William Kemper]

On Fri, 15 Aug 2025 02:37:57 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> Mutators and GC workers have old generation LABs for promotions and old generation evacuations. Priority is given to old evacuations by using a promotion budget. Once the promotion budget is exhausted, a thread local flag is set to disable further promotions (the LAB can still be used for old evacuations). This thread local flag is meant to be cleared to allow all threads to resume promotions on the next cycle. However, this flag is only reset for workers that perform thread root evacuations, which may not be the same workers that perform subsequent evacuations. This patch clears the flag for all threads when their LABs are retired at the end of evacuation.
>
> Marked as reviewed by ysr (Reviewer).

@ysramakrishna - the performance test results show no regressions. The level of detail we need to see the effect of the changes isn't enabled by default in the release testing.

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PR Comment: https://git.openjdk.org/jdk/pull/26785#issuecomment-3192309751